Nowadays, in most aircraft, the calculation of the aeroplane position is performed on the basis of a ground locating system for the airport rolling phases and an in-flight locating system for take-off, landing and cruising flight.
With respect to the ground locating system, generally the latter is handled by a computer, of FMS type, the acronym signifying “Flight Management System”. In particular, the computer fulfils the flight plan display, computation and aeroplane position display functions.
With respect to the ground locating system, generally the latter is handled by another computer, in certain cases called ANS, the acronym standing for “Airport Navigation System”. The latter fulfils the aeroplane map display, computation and ground position display functions.
These two locating systems are nowadays independent inasmuch as they are interfaced with other equipment or systems incorporating sensors that are different depending on whether the aircraft is in the rolling, take-off, stabilized flight or landing phase. Notably, the dynamic aeroplane parameters and the contextual navigation parameters (obstacles, weather, runways, traffic) can differ according to one or other of the navigation systems.
When rolling, the longitudinal speeds are low and can be zero, when stopped, or even negative, in a so-called “pushback” reversing manoeuvre, the lateral speeds are almost zero, except when turning.
Currently, the accuracy of the ground locating systems is of the order of a metre for the rolling phases.
The ground locating system during the rolling phase generally uses sensors of GPS or IRS type, IRS standing for “Inertial Reference System”. This locating system is often coupled, in the airports, with a precision local augmentation system of GBAS type, the acronym standing for “Ground-based augmentation system”. The latter system makes it possible to more accurately locate the aircraft thanks to an error correction done on the ground.
Moreover, this information can be tallied with information originating from antennas fixed to the ground at known positions capable of fixing the aircraft by multilateration. In certain cases, cameras make it possible to view the markings on the ground or even to know the number of turns of the wheels of the landing gears for example.
The ground locating system can also take into account data obtained from the dynamics of the aircraft originating from sensors placed on the braking system or even on the landing gears for example.
In flight, the longitudinal speeds are high, generally above 100 knots, the lateral speed depends on the wind, and can reach 250 knots, and finally the vertical speed is non-zero.
Currently, the accuracies of the in-flight locating systems are of the order of 200 m in approach and greater than a kilometre when cruising.
The in-flight locating system uses, to fix the positioning of the aircraft, mainly equipment comprising sensors of IRS or GPS type and a regional augmentation system of SBAS type, the acronym standing for “Satellite-based augmentation system”. The latter system makes it possible to locate with greater accuracy the aircraft thanks to an error correction made by satellites.
In some cases, it is possible for such equipment to be coupled with a local augmentation system of GBAS type such as an approach configuration for landing.
The in-flight locating system can also use equipment picking up the signals from the radio navigation beacons of VOR or DME type, the acronym DME standing for “Distance Measurement Equipment”.
Nowadays, the in-flight locating systems are more accurate than the ground locating systems when the aircraft is in flight and conversely the ground locating systems are more accurate than the in-flight locating systems when the aircraft is on the ground.
The two systems can be used in any configuration of the aircraft, on the ground or in flight. Generally, the system used is that of the most appropriate context of the aircraft. In other words, in the rolling phase, the crew selects the ground locating system and in the flight phase, of cruising flight type, the crew selects the in-flight locating system.
However, there is a problem in the transitional take-off and landing phase during the changeover from one locating system to the other in which the accuracies of the locating systems do not allow for a continuous changeover of the position of the aircraft. This problem causes trouble for the crew, notably for the display of the aeroplane position when there is a changeover between the display of the airport map and the display of the flight plan.
Moreover, in the take-off phase, there is a problem associated with the offset between the theoretical position, called the designated take-off point, and the actual position of the aircraft on the runway just before throttle-up.
This problem is caused either by the uncertainty concerning the position of the aircraft on the runway relative to the theoretical point, or from an access to the runway via an access ramp not originally planned, a change having been made during the rolling phase. Currently, the crew is responsible for modifying the offset manually in the onboard computer in order to resolve the difference between the theoretical position and the actual position of the aircraft on the runway.
One aim of the invention is to overcome the abovementioned drawbacks.